Spinal stabilization, or immobilization, may become necessary during treatment of a number of illnesses or injures involving the spinal column. Immobilization of the spine may be required to treat spinal fractures, infections affecting the spinal column, tumors associated with the spinal column, and any other injury or illness causing spinal instability. Instability of the spine requires intervention to relieve pain and to maintain neurological function.
Surgical intervention is frequently necessary to immobilize spinal vertebrae, and is particularly suitable in those cases where surgical intervention is required in any event to treat the underlying disease processes, for example, tumors of the spine and vertebral necrosis caused by infectious agents. In such cases, the damaged or necrotic bone is removed, and the remaining bone is resected.
Surgical methods for spinal immobilization may include the placement of bone grafts, or synthetic polymers, to replace necrotic, and/or diseased bone. Such materials may also be implanted in the intervertebral space between adjacent vertebrae to replace damaged discs and immobilize the surrounding vertebrae. Bone grafts require at least several months for fusion, thereby requiring the wearing of extremely uncomfortable and restrictive external stabilization devices, and bone grafts may provide insufficient stabilization in those situations when the graft is not completely successful, or where ongoing treatment interferes with fusion of the graft. Synthetic polymer implants generally also require metal pins or rods to compensate for bonding difficulties, and such implants are difficult to implant and subject to stress fractures. Additionally, the pins may break thereby eliminating any stability produced by the polymer, and the polymer may then move from its implanted position.
Metal spinal fixators, in addition to the metal pins discussed above, are known in the prior art. Such fixators may include bone screws, rods, plates, a combination of screws and plates, and a combination of rods and screws. Bone screws, rods and plates immobilize a vertebra by connecting it to an adjacent vertebra. The rods and plates are generally placed on the outside of the lateral portion of the vertebrae, and the screws are used to secure the position of the plates and rods. One such device is shown in U.S. Pat. No. 3,741,205 which discloses an open frame, rectangular plate secured to the outer anterior aspect of the vertebrae with pins. Another device utilizing rods attached through brackets which are attached by screws to the lateral aspect of the vertebrae is disclosed in U.S. Pat. No. 4,289,123. Such devices are inherently limited because the attachment to the bone generally is made with small screws or pins and is thereby subject to displacement from movement of the spine.
Spinal fixators for insertion in the space between vertebrae are known in the prior art. Such devices are designed to immobilize the spine and to maintain the typical distance between adjacent vertebrae thereby decompressing the spine to relieve pressure on the spinal cord.
One such spinal fixator for insertion between vertebrae is described in U.S. Pat. No. 4,401,112 which teaches a turnbuckle device with terminal spikes. A plate is attached to the turnbuckle and to the anterior aspect of the two adjacent vertebrae. Another spinal fixator is described in U.S. Pat. No. 4,599,086 which discloses a body having two retractable pins inserted between the vertebrae and secured in position with an externally mounted plate and screws.
In addition to the spinal fixators discussed above, other devices exist which are used to replace an intervertebral disc or a meniscus between a joint. A replacement for an intervertebral disc is disclosed in U.S. Pat. No. 4,309,777, and comprises a spring operated insert secured to the adjacent vertebrae with spikes. A resilient, rubber meniscus replacement is shown in U.S. Pat. No. 4,502,161.
A heretofore unmet needs exists for an adjustable spinal fixator that may be easily inserted between two vertebrae for immobilization thereof without the need for additional screws and/or plates to secure the position of the fixator.